1. Field of the Invention
This invention relates to a control system for a cylinder-cutoff internal combustion engine.
2. Description of the Related Art
In an internal combustion engine having a plurality of cylinders, it has been proposed to improve fuel consumption by switching engine operation, based on at least the engine load, between full-cylinder operation during which all of the cylinders are supplied with fuel to be operative and cutoff-cylinder operation during which the fuel supply to some of the cylinders are cut off or stopped to be non-operative. In this type of engine, since shock is occasionally generated due to the fluctuation of torque during engine operation switching, it has been proposed to eliminate shock by adjusting throttle opening during a transitional period of switching, as taught in Japanese Laid-Open Patent Application No. Hei 10 (1998) -103097, for example.
In a vehicle having this type of cylinder cutoff internal combustion engine whose operation is to be switched between full-cylinder operation and cutoff-cylinder operation, when the vehicle runs a downhill during cutoff-cylinder operation, deceleration may occasionally be not enough due to insufficient engine braking effect, or the operator may sometimes feel excessive acceleration depending on the gradient of the downhill.